Radiation imaging apparatus and method for controlling radiation imaging apparatus

ABSTRACT

A radiation imaging apparatus includes a C-arm, a radiation source configured to irradiate a subject with radiation, and a two-dimensional detection device configured to detect the radiation having passed through the subject. The radiation source and the two-dimensional detection device are arranged to face each other across the C-arm, and at least one of the radiation source and the two-dimensional detection device is attached to the C-arm via a sub-arm that is rotatably connected to a frame of the C-arm.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation imaging apparatus, and amethod for controlling the radiation imaging apparatus. Particularly,the present invention is well adaptable to an X-ray imaging apparatuswith a C-arm used in an operating room.

2. Description of the Related Art

An X-ray imaging apparatus with a C-arm used in an operating room isrequired to be capable of freely imaging a portion of a patient to beoperated, and to be capable of executing a computed tomography (CT) withthe rotation at an angle of 180 degrees. In recent years, a function hasbeen demanded from such an imaging apparatus in which an imagingdistance can be changed to be short without fixing the imaging distancefor reducing the X-ray exposure to a patient and operator.

For example, in an X-ray diagnostic apparatus discussed in JapanesePatent Application Laid-Open No. 2000-116631, a multi-joint arm iscoupled to an end of a C-arm to allow an X-ray planar detection deviceto move within the internal space of the C-arm so as to freely image asubject from a multitude of directions without sliding the C-arm.Japanese Patent Application Laid-Open No. 2000-116631 also discusses alink mechanism that movably holds the X-ray planar detection device tothe C-arm.

The X-ray diagnostic apparatus discussed in Japanese Patent ApplicationLaid-Open No. 2000-116631 can freely image the portion of a patient tobe imaged, and enables CT in which the apparatus rotates at an angle of180 degrees. However, the multi-joint arm that is linked to the endportion of the C-arm represents a problem in that it is difficult tocontrol the multi-joint arm to position the X-ray planar detectiondevice at the desired imaging angle. That is, when the X-ray tube isarranged to face the X-ray planar detection device, the multi-jointbecomes a hindrance since it occupies a large space within the C-arm.

An X-ray diagnostic apparatus discussed in Japanese Patent ApplicationLaid-Open No. 2002-336220 includes an X-ray tube, an X-ray detectiondevice, a grid portion arranged on an image-receiving surface of theX-ray detection device, and an arm supporting the X-ray tube and theX-ray detection device to be capable of changing the distance betweenthe X-ray tube and the X-ray detection device.

The X-ray diagnostic apparatus discussed in Japanese Patent ApplicationLaid-Open No. 2002-336220 can change the distance between the X-raysource and the two-dimensional detection device without changing theimaging axis. However, when the length of the distance to be changedincreases, the slide mechanism for changing the length increases, whicharises a problem of substantially increasing the outer dimension of theC-arm. When the outer dimension of the C-arm increases, the apparatus isdifficult to be used in an operating room having a small work area.

SUMMARY OF THE INVENTION

The present invention is directed to a radiation imaging apparatushaving a C-arm and a control method of the radiation imaging apparatuscapable of effectively utilizing the space in the C-arm and capable ofenhancing usability of the radiation imaging apparatus by an operator.

According to an aspect of the present invention, a radiation imagingapparatus includes a C-arm, a radiation source configured to irradiate asubject with radiation, and a two-dimensional detection deviceconfigured to detect the radiation having passed through the subject,wherein the radiation source and the two-dimensional detection deviceare arranged to face each other across the C-arm, and wherein at leastone of the radiation source and the two-dimensional detection device isattached to the C-arm via a sub-arm that is rotatably connected to aframe of the C-arm at the inside from the end portion of the frame.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIGS. 1A and 1B illustrate a configuration of a radiation imagingapparatus.

FIGS. 2A and 2B are side views illustrating when an X-ray tube and atwo-dimensional detection device are moved.

FIGS. 3A and 3B illustrate the movement of the X-ray tube by a shiftunit.

FIGS. 4A and 4B illustrate the position where a sub-arm is connected toa C-arm.

FIGS. 5A and 5B illustrate the case in which the sub-arms are moved inconjunction with each other according to a portion to be imaged.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

An X-ray imaging apparatus is taken as an example of the radiationimaging apparatus in the present exemplary embodiment. However,embodiments of the present invention or modifications thereof may beapplicable to other imaging apparatuses capable of radiating an objector subject with electromagnetic radiation or subatomic particles andconfigured to detect the radiation having passed through the object orsubject. FIG. 1A is a side view illustrating an outer appearance of theX-ray imaging apparatus. FIG. 1B is a diagram illustrating theconfiguration of a main body of the X-ray imaging apparatus.

As illustrated in FIG. 1A, the X-ray imaging apparatus 100 has a mainbody 11. The main body 11 of the X-ray imaging apparatus 100 is providedwith a rotation support portion 12 that supports a slide support portion14. The slide support portion 14 can rotate about the rotation supportportion 12 to a rotation shaft Lh in the horizontal direction indicatedby a two-dot-chain line in FIG. 1A.

The slide support portion 14 in the present exemplary embodiment canrotate about the rotation support portion 12 within a rotation angle ofabout 180 degrees. When the slide support portion 14 is rotated aboutthe rotation support portion 12 at an angle of 180 degrees, the endportions of a semicircular C-arm 13 are exchanged as illustrated in FIG.2B.

A bed 30 for a subject (patient) is arranged between the end portions ofthe C-arm 13. When the C-arm 13 is rotated at 180 degrees, an imagingmethod (under-tube), in which an X-ray is generated from the back of thesubject who is in the supine position, and an imaging method(over-tube), in which an X-ray is generated from the front of thesubject who is in the supine position, can be executed.

The slide support portion 14 supports the C-arm 13 in such a manner thatthe C-arm 13 can slide along the shape of the frame of the C-arm 13 in adirection indicated by an arrow A or a direction indicated by an arrow Bin FIG. 1A, so as to trace a substantially semicircular path concentricto the C-arm 13. The slide angle of the slide support portion 14 is setto the angle capable of executing CT imaging.

Specifically, the slide angle is desirably set to the angle obtained byadding an X-ray fan angle to 180 degrees, i.e., not less than 180degrees. The fan angle means the spread of the X-ray emitted from anX-ray tube 16 in the horizontal direction. When the CT is not needed,the slide angle may be set to 180 degrees.

Accordingly, the C-arm 13 slides at least in the A direction at 90degrees or in the B direction at 90 degrees from the state illustratedin FIG. 1A. Since the C-arm 13 slides to the slide support portion 14,the subject can be imaged from both sides of the subject who is in thesupine position or in the recumbent position.

The X-ray tube 16 serving as a radiation source is arranged at one endportion of the frame of the C-arm 13 through a first sub-arm 15. Thefirst sub-arm 15 is pivotably connected by a first joint 19 a. The firstjoint 19 a is provided at the portion on the frame of the C-arm. 13inward from one end portion of the C-arm 13 and serves as a connectionportion.

The first joint 19 a is a rotation mechanism. The first joint 19 a is,for example, a horizontally arranged link shaft. A tube mounting portion22 serving as a mounting portion of the X-ray tube 16 is pivotablyconnected, through a second joint 19 b, to the end portion of the firstsub-arm 15 opposite to the first joint 19 a. The second joint 19 b isalso a rotation mechanism, and it is, for example, a horizontallyarranged link shaft.

The tube mounting portion 22 has a grip 26 that is used to move theX-ray tube 16 by an operator. The X-ray tube 16 is mounted on the tubemounting portion 22 through a below-described shift portion 28. Asdescribed above, the X-ray tube 16 serving as the radiation source isprovided at one end portion of the frame of the C-arm 13 through thefirst sub-arm 15.

Since the first joint 19 a and the second joint 19 b are thehorizontally arranged link shafts, the first sub-arm 15 and the X-raytube 16 can move in the plane formed by the frame of the C-arm 13.

A two-dimensional detection device 18 that detects the X-ray, which isemitted from the X-ray tube 16 and passes through the subject, isarranged at the other end portion of the frame of the C-arm 13 through asecond sub-arm 17. The second sub-arm 17 is pivotably connected by athird joint 19 c, which is provided at the portion on the frame of theC-arm 13 inward from the other end portion of the C-arm 13 and whichserves as a connection portion.

The third joint 19 c is a rotation mechanism. The third joint 19 c is,for example, a horizontally arranged link shaft. A detection devicemounting portion 23 serving as a mounting portion of the two-dimensionaldetection device 18 is pivotably connected, through a fourth joint 19 d,to the end portion of the second sub-arm 17 opposite to the third joint19 c.

The fourth joint 19 d is a rotation mechanism, and it is, for example, ahorizontally arranged link shaft. The detection device mounting portion23 has a grip 27 that is used to move the two-dimensional detectiondevice 18 by an operator. The two-dimensional detection device 18 ismounted on the detection device mounting portion 23 through abelow-described shift portion 29. As described above, thetwo-dimensional detection device 18 that detects the X-ray emitted fromthe X-ray tube 16 is provided at the other end portion of the frame ofthe C-arm 13 through the second sub-arm 17.

Since the third joint 19 c and the fourth joint 19 d are thehorizontally arranged link shafts, the second sub-arm 17 and thetwo-dimensional detection device 18 can move in the plane formed by theframe of the C-arm 13.

With this configuration, the X-ray tube 16 and the two-dimensionaldetection device 18 are arranged to face each other at both end portionsof the C-arm 13 across the bed 30 of the subject indicated by a chainline in FIG. 1A.

The configuration of the main body 11 of the X-ray imaging apparatus 100will be described with reference to FIG. 1B. As illustrated in FIG. 1B,the main body 11 includes a control unit 50, an image processing unit51, a storage unit 52, a high-voltage generation unit 53, an operationunit 54, and a display unit 55. The control unit 50 controls the overalloperation of the X-ray imaging apparatus 100. Specifically, the controlunit 50 executes a program stored in the storage unit 52 according to aselection of a mode.

The image processing unit 51 converts the X-ray data detected by thetwo-dimensional detection device 18 into image data that can beconfirmed or stored by the operator. The storage unit 52 is alarge-capacity storage medium and a memory such as a random accessmemory (RAM) or a read-only memory (ROM). The storage unit 52 stores theprogram according to the mode, or is used as a work memory by thecontrol unit 50.

The high-voltage generation unit 53 supplies high voltage to the X-raytube 16. The operation unit 54 includes various operation switches. Thedisplay unit 55 is a display on which the image data converted by theimage processing unit 51 is displayed.

The rotation angle of the first sub-arm 15 and the second sub-arm 17will next be described.

The rotation angles of the first sub-arm 15 and the second sub-arm 17are determined according to various factors. The factors include, forexample, the grid portion 24 arranged on the front surface(image-receiving surface) of the two-dimensional detection device 18,the X-ray diaphragm 25 arranged at the front surface of the X-ray tube16, the relationship between the diameter of the frame of the C-arm 13and the lengths of the respective sub-arms, etc.

The grid portion 24 arranged at the front surface of the two-dimensionaldetection device 18 has a function of eliminating (e.g., blocking,absorbing or deflecting) scattered rays of the X-ray, for example, bycutting off diagonally incident X-rays. The grid portion 24 has a thinlead plate with strips arranged thereon at a constant distance. Morespecifically, there are various types of grids (e.g., focused, parallel,criss-crossed, etc) that may be used as the grid portion 24. Each typeof grid can determine certain aspect (e.g., grid ratio, grid density,focal range, etc) of the grid portion 24. In a focused grid, forexample, strips of radiation-absorbing material are arranged at apredetermined distance from each other and tilted progressively from thecenter to the outer edge thereof. Radiation rays passing through each ofthese strips converge at a point known as the grid focus. For optimalimaging, it is desirable that the grid focus substantially matches thedistance between the focal point of the X-ray generation portion and thedetecting surface (SID) of the X-ray detection device.

When the convergent distance of the grid portion is defined as f0 asillustrated in FIG. 1A, the limit of the usage distance of the gridportion 24 is set to include the convergent distance f0 within a usablerange thereof. When the lower limit of the usage distance is defined asf1, and the upper limit of the usage distance is defined as f2, theequation of f1=<f0=<f2 is established.

The X-ray photography cannot be executed with the X-ray tube 16 and thetwo-dimensional detection device 18 being made closer to each other withthe distance shorter than the lower limit f1 or higher than the upperlimit f2 of the usage distance of the grid portion 24. Therefore, thefirst to fourth joints 19 a to 19 d regulate the rotation, through thefirst sub-arm 15, the second sub-arm 17, the tube mounting portion 22,and the detection device mounting portion 23, to prevent the distancebetween the X-ray tube 16 and the two-dimensional detection device 18from being shorter than the lower limit f1 of the usage distance.

The X-ray diaphragm 25 arranged at the front surface of the X-ray tube16 regulates the X-ray irradiation range to irradiate only the portionneeded for the diagnosis, which prevents the subject from beingunnecessarily exposed to the radiation. On the other hand, the X-raydiaphragm 25 increases the X-ray irradiation range to be capable ofobserving the portion needed for the diagnosis at a time. Therefore, thelimit of the near distance between the X-ray tube 16 and thetwo-dimensional detection device 18 is determined in the minimum area orthe maximum area that can be set by the X-ray diaphragm 25.

As described above, the rotation angles of the first to fourth joints 19a to 19 d are determined by the characteristic of the grid portion 24 orthe X-ray diaphragm 25.

In the above description, the first sub-arm 15 and the second sub-arm.17 are moved in the plane formed by the frame of the C-arm. 13. However,the present invention is not limited thereto. For example, it can beconfigured so that the first sub-arm 15 and the second sub-arm 17 can bemoved in the direction substantially perpendicular to the plane formedby the frame of the C-arm 13.

In this case, a fifth joint and a sixth joint, which allow therespective sub-arms to pivot in the direction perpendicular to theplane, may be added between the C-arm 13 and the respective sub-arms.

This configuration can easily move the imaging area on the subject inthe body axis of the subject. Specifically, the X-ray tube 16 and thetwo-dimensional detection device 18 can be moved in the body axisdirection of the subject, whereby the operator can easily execute X-rayphotography without moving the main body 11.

The case in which the distance between the X-ray tube 16 and thetwo-dimensional detection device 18 is changed, i.e., in which theimaging distance is changed, will next be described. A brake releaseswitch (not illustrated) is provided at the position proximate to thegrips 26 and 27 at the end of the tube mounting portion 22 and at theend of the detection device mounting portion 23.

When the operator presses the brake release switch while gripping thegrip 27 at the two-dimensional detection device 18, for example, thebrake of the rotation mechanism made of the third joint 19 c and thefourth joint 19 d can be released. When the operator grips the grip 27with the brake being released, and moves the two-dimensional detectiondevice 18 close to the X-ray tube 16 as illustrated in FIG. 2A, theimaging distance can be changed.

In the present exemplary embodiment, the imaging distance is changedbased on the condition that the X-ray light flux from the X-ray tube 16is not diagonally incident on the two-dimensional detection device 18,i.e., that the X-ray tube 16 and the two-dimensional detection device 18move parallel to each other in such a manner that the front surface ofthe two-dimensional detection device 18 is always orthogonal to theimaging axis Lc illustrated in FIG. 1A. The imaging axis Lc is a linelinking the focal point of the X-ray tube 16 and the center of thetwo-dimensional detection device 18.

The rotation angles of the third joint 19 c and the fourth joint 19 dcan uniquely be determined through the parallel movement of thetwo-dimensional detection device 18 to allow the front surface of thetwo-dimensional detection device 18 to be always orthogonal to theimaging axis Lc. Therefore, the second sub-arm 17 and the detectiondevice mounting portion 23 can easily be controlled.

The provision of the second sub-arm 17 can increase the space in theC-arm 13 when the imaging distance is increased or decreased. Thedetection device mounting portion 23 is not limited to be providedthrough the third joint 19 c, the second sub-arm 17, and the fourthjoint 19 d. The detection device mounting portion 23 may be providedthrough two or more joints (rotation mechanism).

Similarly, the brake of the rotation mechanism by the first joint 19 aand the second joint 19 b can be released, when the operator press thebrake release switch while gripping the grip 26 at the X-ray tube 16.When the operator grips the grip 26 with the brake being released, andmoves the X-ray tube 16 close to the two-dimensional detection device 18as illustrated in FIG. 2B, the imaging distance can be changed.

The rotation angles of the first joint 19 a and the second joint 19 bcan uniquely be determined through the parallel movement of the X-raytube 16 to allow the front surface of the two-dimensional detectiondevice 18 to be always orthogonal to the imaging axis Lc. Therefore, thefirst sub-arm 15 and the tube mounting portion 22 can easily becontrolled.

The provision of the first sub-arm 15 can increase the space in theC-arm 13 when the imaging distance is increased or decreased.

The tube mounting portion 22 is not limited to be provided through thefirst joint 19 a, the first sub-arm. 15, and the second joint 19 b. Thetube mounting portion 22 may be provided through two or more joints(rotation mechanism).

As described above, the X-ray light flux from the X-ray tube 16 isprevented from being diagonally incident on the two-dimensionaldetection device 18. Therefore, the grid portion 24 does not cut off theX-ray that is effective for the diagnosis, with the result that aneffective X-ray photography can be carried out. There are two modes forthe control of preventing the diagonal incidence of the X-ray lightflux.

One of them is a mode (active-side control mode) for controlling thetwo-dimensional detection device 18 in such a manner that a verticalline to the front surface of the two-dimensional detection device 18passes through the focal point of the X-ray tube 16 when the operatorchanges the imaging distance while holding the grip 27 of the detectiondevice mounting portion 23. In the active-side control mode, when theoperator changes the imaging distance while holding, in contrast, thegrip 26 at the tube mounting portion 22, the X-ray tube 16 is controlledin such a manner that the vertical line to the front surface of thetwo-dimensional detection device 18 passes through the focal point ofthe X-ray tube 16.

The other one is a mode (passive-side control mode) for controlling theX-ray tube 16 in such a manner that a vertical line to the front surfaceof the two-dimensional detection device 18 passes through the focalpoint of the X-ray tube 16 when the operator changes the imagingdistance while holding the grip 27 of the detection device mountingportion 23. In the passive-side control mode, when the operator changesthe imaging distance while holding, in contrast, the grip 26 at the tubemounting portion 22, the two-dimensional detection device 18 iscontrolled in such a manner that the vertical line to the front surfaceof the two-dimensional detection device 18 passes through the focalpoint of the X-ray tube 16.

The merit of the active-side control mode is that the incident angle ofthe X-ray to the subject is easy to be kept when the detection devicemounting portion 23 is moved. The merit of the passive-side control modeis that, when the operator moves the detection device mounting portion23 while holding the grip 27, the operator does not feel torque from thesecond sub-arm 17 or other components. The above-mentioned two modes areswitched by the control unit 50 according to the setting made by theoperator when operating the operation unit 54.

The two-dimensional detection device 18 and the X-ray tube 16 in thepresent exemplary embodiment can move in conjunction with each other.More specifically, the X-ray imaging apparatus 100 can be configuredsuch that the first sub-arm 15 automatically moves in conjunction withthe second sub-arm 17. The second sub-arm 17 automatically moves inconjunction with the first sub-arm 15.

A mode changeover switch (not illustrated) is provided at the positionproximate to either one of the grips 26 and 27. The operator can changethe mode to a single mode or conjunction mode by the mode changeoverswitch.

In the single mode, only one of the sub-arms 15 and 17, which is at theside of the grips 26 or 27 that is held by the operator, and only one ofthe detection device mounting portion 23 and the tube mounting portion22, which is at the side of the grips 26 or 27 that is held by theoperator, move.

On the other hand, in the conjunction mode, one of the sub-arms 15 and17, which is at the side of the grips 26 or 27 that is not held by theoperator, and one of the detection device mounting portion 23 and thetube mounting portion 22, which is at the side of the grips 26 or 27that is not held by the operator, also move in conjunction with theother sub-arm and the other mounting portion. The control unit 50changes the mode between the single mode and the conjunction modeaccording to the setting of the mode changeover switch.

The conjunction mode includes two types of modes, which are a constantimaging-distance conjunction mode and a variable imaging-distanceconjunction mode.

In the constant imaging-distance conjunction mode, the sub-arm 15 or 17at the side of the grip 26 or 27 that is not held by the operator andthe mounting portion at the side of the grip 26 or 27 that is not heldby the operator move in conjunction with each other so as not to changethe imaging distance. Specifically, in the constant imaging-distanceconjunction mode, each of the sub-arms 15 and 17 and each of themounting portions 22 and 23 move, respectively in conjunction with eachother, to allow the imaging distance between the two-dimensionaldetection device 18 and the X-ray tube 16 to be constant.

For example, as the two-dimensional detection device 18, i.e., thesecond sub-arm 17, is moved away from the subject, the X-ray tube 16,i.e., the first sub-arm 15 moves close to the subject. In this case, theimaging area is decreased to be capable of increasing the magnificationratio of the subject without changing the aperture of the X-raydiaphragm 25 and the imaging distance.

On the other hand, as the two-dimensional detection device 18, i.e., thesecond sub-arm 17, is moved close to the subject, the X-ray tube 16,i.e., the first sub-arm 17, moves away from the subject. In this case,the imaging area is increased to be capable of decreasing themagnification ratio of the subject, but the imaging distance ismaintained substantially constant.

In the variable imaging-distance conjunction mode, the sub-arm 15 or 17at the side of the grip 26 or 27 that is not held by the operator andthe mounting portion at the side of the grip 26 or 27 that is not heldby the operator move in conjunction with each other so as to change theimaging distance. Specifically, in the variable imaging-distanceconjunction mode, each of the sub-arms 15 and 17 and each of themounting portions 22 and 23 move so that the two-dimensional detectiondevice 18 and the X-ray tube 16 move in reverse direction with respectto each other.

For example, as the two-dimensional detection device 18, i.e., thesecond sub-arm 17, is moved away (to be apart) from the subject, theX-ray tube 16, i.e., the first sub-arm 15, is also moved away (to beapart) from the subject. In this case, the imaging area is changed withthe magnification ratio being maintained substantially constant.

On the other hand, as the two-dimensional detection device 18, i.e., thesecond sub-arm 17, is moved towards (to be close to) the subject, theX-ray tube 16, i.e., the first sub-arm 17, is also moved towards (to beclose to) the subject. In this case, the imaging area is changed withthe magnification ratio being maintained substantially constant.Specifically, when the operator moves the two-dimensional detectiondevice 18 from the position indicated by a broken line to the positionindicated by a solid line in FIG. 2A as holding the grip 27, the X-raytube 16 is moved from the position indicated by the broken line to theposition indicated by the solid line.

The operation described above is controlled according to the instructionfrom the control unit 50. Specifically, when the control unit 50 detectsthe movement of the second sub-arm 17 (i.e., the rotation angle of thethird joint 19 c) at the side of the grip 27 held by the operator, thecontrol unit 50 calculates the rotation angle for rotating the firstjoint 19 a according to the detected rotation angle of the third joint19 c.

The first joint 19 a rotates the first sub-arm 15 based on thecalculated rotation angle of the third joint 19 c. The second joint 19 brotates the tube mounting portion 22, i.e., the X-ray tube 16, accordingto the rotation angle of the first joint 19 a. On the other hand, whenthe first sub-arm 15 is moved, the third joint 19 c rotates the secondsub-arm 17 based on the calculated rotation angle.

The fourth joint 19 d rotates the detection device mounting portion 23,i.e., the two-dimensional detection device 18, according to the rotationangle of the third joint 19 c. In this manner, the respective joints 19a to 19 d move in conjunction the two-dimensional detection device 18and the X-ray tube 16 in the reverse direction to make the distancevariable, or move them simultaneously in the same direction to allow theimaging distance between the two-dimensional detection device 18 and theX-ray tube 16 to be constant.

The control unit 50 switches from the constant imaging-distanceconjunction mode to the variable imaging-distance conjunction mode andvice versa according to the setting of the mode changeover switch. Theprocess described above is realized, according to the selected mode,through the execution of specific program steps of a program stored inthe storage unit 52.

It is advantageous to move the two-dimensional detection device 18 andthe X-ray tube 16 in conjunction with each other based on the portion,which is to be imaged, of the subject. This will be described below.

A shift portion 28 (radiation source shift portion) mounted on the tubemounting portion 22 will be described with reference to FIGS. 3A and 3B.The shift process by the shift portion described below is the so-calledactive-side control mode.

In the present exemplary embodiment, the first sub-arm 15 and the secondsub-arm 17 are connected to the frame of the C-arm 13 at the inside ofthe C-arm 13 via the first joint 19 a and the second joint 19 c. Thefirst joint 19 a and the second joint 19 c rotate the first sub-arm 15and the second sub-arm 17, respectively, so that the imaging distance(i.e., the distance between the detection device 18 and the X-ray tube16) is changed. Therefore, since the first sub-arm 15 and the secondsub-arm 17 move in the space between the two ends of the C-arm 13, evenif the imaging distance is increased, the outer shape of the C-arm isnot substantially increased.

However, the positional relationship between the line segment linkingthe X-ray tube 16 and the center of the two-dimensional detection device18 and the C-arm 13 might be changed according to the change in theimaging distance.

As illustrated in FIG. 3A, the line segment linking the X-ray tube 16and the center of the two-dimensional detection device 18 is defined asthe imaging axis Lc with the state in which the first sub-arm 15 and thesecond sub-arm 17 are rotated to allow the X-ray tube 16 and thetwo-dimensional detection device 18 to be very close to each other. Inthe present exemplary embodiment, the imaging axis Lc is the same as theline linking both ends of the C-arm 13.

In the present exemplary embodiment, the X-ray tube 16 is arranged atthe upper side, while the two-dimensional detection device 18 isarranged at the lower side as illustrated in FIG. 3A.

In the position illustrated in FIG. 3A, is assumed that the operatormoves the first sub-arm 15 indicated by the solid line to be close tothe frame of the C-arm. 13, i.e., moves the sub-arm 15 indicated by thesolid line to the position indicated by the broken line.

In this case, the first sub-arm 15 is rotated in the clockwise directionabout the first joint 19 a, so that the second joint 19 b moves in theupper-right direction. Therefore, the center of the X-ray tube 16 movesto the right from the imaging axis Lc. Accordingly, the line segmentlinking the X-ray tube 16 and the center of the two-dimensionaldetection device 18 is shifted away from the imaging axis Lc, wherebythe X-ray photography in the imaging range desired by the operatorcannot be executed.

Accordingly, the X-ray tube 16 has to be shifted in the directionorthogonal to the imaging axis Lc, i.e., shifted to the left asillustrated by the arrow in FIG. 3B, to allow the line segment linkingthe X-ray tube 16 and the center of the two-dimensional detection device18 to coincide with the imaging axis Lc.

The shift portion 28 has a function of shifting the X-ray tube 16 in thedirection orthogonal to the imaging axis Lc and in the direction of theplane formed by the frame of the C-arm 13 to the tube mounting portion22. The shift portion 28 is, for example, a ball screw or alinear-moving slide apparatus.

The shift portion 28 shifts the X-ray tube 16 in the direction towardthe inside of the C-arm 13 when the imaging distance is decreased, whileshifts the X-ray tube 16 in the direction toward the outside of theC-arm 13 when the imaging distance is increased. The shift amount of theshift portion 28 for shifting the X-ray tube 16 is calculated by thecontrol unit 50.

Specifically, the control unit 50 detects the movement of the firstsub-arm 15, i.e., the rotation angle of the first joint 19 a, andcalculates the shift amount according to the detected rotation angle. Acorrespondence table or the like is stored in the storage unit 52beforehand, and the shift amount according to the rotation angle may becalculated based on the correspondence table by the control unit 50. Inthis manner, the shift portion 28 shifts the X-ray tube 16 orthogonal tothe imaging axis Lc in accordance with the rotation angle of at leastone of the joints 19 a to 19 d.

As described above, the shift portion 28 shifts the X-ray tube 16 basedon the shift amount calculated by the control unit 50, thereby allowingthe line segment linking the X-ray tube 16 and the center of thetwo-dimensional detection device 18 to agree with the imaging axis Lc asillustrated in FIG. 3B. Thus, the shift portion 28 can move the focalpoint of the X-ray tube 16 to the imaging axis Lc.

In the above description, the shift portion 28 shifts the X-ray tube 16.A shift portion (detection device shift portion) 29 similarly shifts thetwo-dimensional detection device 18 in the direction orthogonal to theimaging axis Lc.

The shift portion 29 shifts the two-dimensional detection device 18 inthe direction toward the inside of the C-arm 13 when the imagingdistance is decreased, while it shifts the two-dimensional detectiondevice 18 in the direction toward the outside of the C-arm 13 when theimaging distance is increased. The shift amount of the shift portion 29for shifting the two-dimensional detection device 18 is calculated bythe control unit 50 in the same manner as described above in referenceto the shift portion 28.

As described above, the shift portion 29 shifts the two-dimensionaldetection device 18 based on the shift amount calculated by the controlunit 50, thereby allowing the line segment linking the X-ray tube 16 andthe center of the two-dimensional detection device 18 to coincide withthe imaging axis Lc. Thus, the shift portion 29 can move the center ofthe two-dimensional detection device 18 to the imaging axis Lc.

The operations of the shift portions 28 and 29 are different accordingto the set mode. Specifically, when the detection device mountingportion 23 is moved to change the imaging distance when the conjunctionmode is set by the mode changeover switch described above, the firstsub-arm. 15 and the tube mounting portion 22 also move in conjunctionwith the detection device mounting portion 23. Therefore, the shiftportion 29 shifts the two-dimensional detection device 18, while theshift portion 28 shifts the X-ray tube 16.

On the other hand, even if the detection device mounting portion 23 ismoved to change the imaging distance when the single mode is set, theshift portion 29, which is at the moved side, only shifts thetwo-dimensional detection device 18.

In the above description, at least one of the X-ray tube 16 and thetwo-dimensional detection device 18 is shifted so that the centerthereof can be aligned with the imaging axis Lc, which is the linesegment linking the X-ray tube 16 and the center of the two-dimensionaldetection device 18. However, the present invention is not limitedthereto.

Another shifting manner by the shift portions 28 and 29 will bedescribed below. The shifting manner described below is the so-calledpassive-side control mode.

For example, when the operator moves the two-dimensional detectiondevice 18, the center of the two-dimensional detection device 18 moves,so that a new imaging axis passing the center of the two-dimensionaldetection device 18 is passively determined. Therefore, the shiftportion 28 at the X-ray tube 16 shifts the X-ray tube 16 to agree withthe new imaging axis.

On the other hand, when the operator moves the X-ray tube 16, the center(focal point) of the X-ray tube 16 moves, so that a new imaging axispassing the center of the X-ray tube 16 is passively determined.Therefore, the shift portion 29 at the two-dimensional detection device18 shifts the two-dimensional detection device 18 to agree with the newimaging axis.

The shift amount of the shift portions 28 and 29 for shifting the X-raytube 16 or the two-dimensional detection device 18 is calculated by thecontrol unit 50. Specifically, the control unit 50 detects the movementof the first sub-arm 15, i.e., the rotation angle of the first joint 19a, and calculates the position of the new imaging axis according to thedetected rotation angle.

The control unit 50 further calculates the shift amount for shifting thetwo-dimensional detection device 18 that agrees with the calculatedimaging axis. The shift portion 29 at the two-dimensional detectiondevice 18 shifts the two-dimensional detection device 18 based on thecalculated shift amount. On the other hand, when the second sub-arm 17is moved, the control unit 50 calculates the shift amount of the X-raytube 16.

The shift portion 28 at the X-ray tube 16 shifts the X-ray tube 16 basedon the calculated shift amount. The process described above is realizedby the execution of the program according to the mode stored in thestorage unit 52.

As described above, in the so-called passive-side control mode, theX-ray tube 16 or the two-dimensional detection device 18 at the sidemoved by the operator is not automatically shifted. Therefore, the X-raytube 16 or the two-dimensional detection device 18 is easily positioned.

In the above description, the shift portions 28 and 29 are mounted onthe tube mounting portion 22 and the detection device mounting portion23 respectively. However, the present invention is not limited thereto.Specifically, the shift portions 28 and 29 may optionally be configured,so long as they can move the X-ray tube 16 and the two-dimensionaldetection device 18 with respect to the respective sub-arms.

A preferable range of the position on the frame of the C-arm 13 wherethe first sub-arm 15 and the second sub-arm 17 are provided will next bedescribed with reference to FIGS. 4A and 4B.

One of the factors for determining the positional range is the gridportion 24. When the convergent distance of the grid portion 24 isdefined as f0, the limit of the usage distance of the grid portion 24 isset to include the convergent distance f0.

When the lower limit of the usage distance is defined as f1, and theupper limit of the usage distance is defined as f2, the equation off1=<f0=<f2 is established. The limit of the usage distance f1=<f0=<f2represents the range where the amount of cutting off the X-ray that iseffective for the X-ray photography by the grid portion 24 is not morethan a specified value. At the portion without the range describedabove, the subject is exposed to the radiation more than necessary, sothat this range is not preferable for the X-ray photography.

The first sub-arm 15 and the second sub-arm 17 are generally desirableto be short. However, when they are too short, the interference problembetween the X-ray tube 16 and the two-dimensional detection device 18arises. Therefore, there are preferable ranges for the positions of thefirst joint 19 a and the third joint 19 c.

The factor for determining the range of the link position is the lowerlimit f1 of the usage distance. As illustrated in FIG. 4A, when thecentral point of the semicircular C-arm 13 is defined as O, the anglefrom the end portion of the C-arm 13 to the first joint 19 a is definedas α1.

The end portion of the C-arm 13, in the present exemplary embodiment, ispreferably aligned with the crossing portion where the imaging axis Lclinking the X-ray tube 16 and the center of the two-dimensionaldetection device 18 and the C-arm 13 cross or substantially cross. Theposition of the first joint 19 a with the angle α1 is the positionenabling the shortest sub-arm.

The angle α1 is set so that the distance L1 between the first joint 19 aand the second joint 19 b is equal to the distance L2 between the firstjoint 19 a and the end portion of the C-arm 13. In the abovedescription, the number of the joints between the first sub-arm 15 andthe tube mounting portion 22 is one. When there are plural joints, thedistance between the first joint 19 a and the joint farthest from thefirst joint 19 a is defined as the distance L1.

When the distance from the central point O to one end portion of theC-arm 13 is defined as the radius R, the equation below is established.

L1=L2   (1)

2R=f1+L1×cos(α1)   (2)

Specifically, the angle α1 that sets the distance L1 of the shortestsub-arm for establishing the equations (1) and (2) is selected.

Next, an angle α2 that sets the longest sub-arm is specified. The limitwhen the sub-arm is set to be longest is specified by the usability ofthe C-arm 13. Specifically, when the first sub-arm 15 is unnecessarilylong, the space in the frame of the C-arm 13, i.e., the arc space isreduced.

As the arc space formed by the C-arm 13 is decreased, the space occupiedby the subject is decreased. In view of this, the angle α2 is specifiedby the equation described below from the relationship illustrated inFIG. 4B, supposing that the cross-section of the subject is a rectangle.

f1=R×(1+cos(α2))   (3)

Consequently, when the angle from one end portion of the C-arm 13 to thefirst joint 19 a is defined as α, the range where the first joint 19 acan be provided is represented by α1≦α≦α2. In FIGS. 4A and 4B, the firstsub-arm 15 is taken as an example. However, the range where the thirdjoint 19 c is provided is similarly specified for the second sub-arm 17holding the two-dimensional detection device 18.

In the above description, the case in which only one of the sub-arms 15and 17 move is described, since the lower limit f1 of the imagingdistance can be realized by moving only one of the sub-arms 15 and 17when the single mode is set.

As described above, the factor for regulating the range where the firstjoint 19 a and the third joint 19 c are provided is the lower limit f1of the imaging distance of the usage distance. Specifically, when thelower limit f1 of the imaging distance of the grid portion 24, which ismounted on the front surface of the two-dimensional detection device 18,is changed, the range where the first joint 19 a and the third joint 19c can be provided also changes.

Therefore, the X-ray imaging apparatus 100 can be configured such thatthe lower limit f1 of the imaging distance of the grid portion 24 can beinput by the operator through the operation unit 54 on the main body 11.The control unit 50 calculates the position where the first joint 19 aand the third joint 19 c move along the frame of the C-arm 13 accordingto the input lower limit f1 of the imaging distance.

It may be configured so that the first joint 19 a and the third joint 19c move along the frame of the C-arm 13 in the direction indicated by anarrow C in FIG. 4B to be located at the calculated position. The movingrange of the unit to move the joints is restricted according to therange of the shifted distance by the shift portions 28 and 29.

In the above description, the mode is switched to the single mode or theconjunction mode by the mode changeover switch, and in the conjunctionmode, the first sub-arm 15 and the second sub-arm 17 move in conjunctionwith each other.

The case in which the sub-arm is controlled based on imaged-portioninformation will next be described with reference to FIGS. 5A and 5B.The imaged portion indicates, for example, a patient's body part such asa spine, an abdomen, a head, four limbs (thigh, brachium, etc.), or thelike. The control unit 50 acquires the imaged-portion information inputby the operator through the operation unit 54 or receives theimaged-portion information according to Digital Imaging andCommunications in Medicine (DICOM) standard from a network input unit(not illustrated).

The control unit 50 outputs the captured image data to the otherexternal apparatus according to the DICOM standard.

It is supposed here that a spine is operated as an area of interest 31of the subject as illustrated in FIG. 5A. In this case, even if the modeis set to the conjunction mode by the mode changeover switch, it is notpreferable that the first sub-arm 15 and the second sub-arm 17 move inconjunction with each other, because there is no moving space.

On the other hand, it is supposed here that a head is operated as thearea of interest 31 of the subject as illustrated in FIG. 5B. In thiscase, when the mode is set to the conjunction mode by the modechangeover switch, it is preferable that the first sub-arm 15 and thesecond sub-arm 17 move in conjunction with each other because there issufficient moving space around of the subject being imaged. As describedabove, it may be determined based on the imaged-portion informationwhether the first sub-arm 15 and the second sub-arm 17 move inconjunction with each other.

In the above description, when the lower limit f1 of the imagingdistance of the grid portion 24 is changed, the first joint 19 a and thethird joint 19 c move along the frame of the C-arm 13.

The case in which the first joint 19 a and the third joint 19 c movebased on the imaged-portion information will be described below. It issupposed that the control unit 50 acquires the imaged-portioninformation, and determines that the imaged portion is the portionhaving a large sectional area, such as a spine or abdomen. In this case,at least either one of the first joint 19 a and the third joint 19 cmove toward the end portion of the C-arm 13 along the frame of the C-arm13 to increase the arc space of the C-arm 13 under the instruction fromthe control unit 50.

On the other hand, the control unit 50 may determine that the imagedportion is the portion having a small sectional area, such as fourlimbs. In this case, at least either one of the first joint 19 a and thethird joint 19 c move toward the inside of the C-arm 13 along the frameof the C-arm 13 to decrease the arc space of the C-arm 13 under theinstruction from the control unit 50.

As described above, the first joint 19 a or the third joint 19 c movesaccording to the imaged portion to move the first sub-arm 15 or thesecond sub-arm 17, whereby the arc space of the C-arm 13 according tothe imaged portion can be changed.

The relationship between the arranging direction of lead plates thatconstitute the grid portion 24 and the direction of shifting thetwo-dimensional detection device 18 and the X-ray tube 16 by the shiftportions 28 and 29 will next be described.

The grid portion 24 is formed by arranging plural lead plates (strips)with a predetermined space therebetween. Specifically, the arrangingdirection (hereinafter referred to as stripe direction) of the leadplates means the direction orthogonal to the direction in which the gapsbetween the lead plates are continued. In the present exemplaryembodiment, the shift portions 28 and 29 shift the X-ray tube 16 or thetwo-dimensional detection device 18 in the direction orthogonal to thestripe direction of the grid portion 24.

Specifically, the shift portions 28 and 29 align the X-ray tube 16 orthe two-dimensional detection device 18 in such a manner that thevertical line from the center of the two-dimensional detection device 18passes through the center of the X-ray tube 16.

The lead plates of the grid portion 24 are arranged to be converged inthe stripe direction. Therefore, when the alignment is shifted in thestripe direction, the cut-off of the X-ray is increased. Accordingly,the cut-off of the X-ray, which is effective for the diagnosis, isdesensitized to the misalignment.

The respective units constituting the radiation imaging apparatus andthe respective steps in the control process of the radiation imagingapparatus in the exemplary embodiment of the present invention can berealized by the execution of the program stored in the RAM or ROM of thecontrol unit 50 (computer). The program and the computer-readablerecording medium having the program recorded thereon are included in andmake part of the present invention.

The present invention can be embodied in the form of a system, anapparatus, a method, a program, or a tangible non-transitory recordingmedium. Specifically, the present invention can applicable to anapparatus including one device or a plurality of devices.

The present invention supplies the program of software realizing thefunction of the above-mentioned exemplary embodiment directly to asystem or an apparatus, or remotely to a system or an apparatus. Thepresent invention includes the case in which the present invention isachieved by reading and executing the supplied program code by thecomputer in the system or the apparatus.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent ApplicationLaid-Open No. 2009-133382 filed Jun. 2, 2009, which is herebyincorporated by reference herein in its entirety.

1. A radiation imaging apparatus comprising: a C-arm; a radiation sourceconfigured to irradiate a subject with radiation; and a two-dimensionaldetection device configured to detect the radiation having passedthrough the subject, wherein the radiation source and thetwo-dimensional detection device are arranged to face each other acrossthe C-arm, and wherein at least one of the radiation source and thetwo-dimensional detection device is attached to the C-arm via a sub-armthat is rotatably connected to a frame of the C-arm at the inside froman end portion of the frame.
 2. The radiation imaging apparatusaccording to claim 1, wherein the radiation source is attached to theC-arm via a first sub-arm that is rotatably connected to the frame ofthe C-arm at the inside from one end portion of the frame, and whereinthe two-dimensional detection device is attached to the C-arm via asecond sub-arm that is rotatably connected to the frame of the C-arm atthe inside from the other end portion of the frame.
 3. The radiationimaging apparatus according to claims 2, further comprising: a radiationsource shift unit provided between the radiation source and the firstsub-arm and configured to move the radiation source towards the firstsub-arm, wherein the radiation source shift unit moves the radiationsource according to an angle of rotation of the first sub-arm tomaintain the radiation source aligned with an imaging axis that linksthe radiation source, which has not yet been moved, and thetwo-dimensional detection device.
 4. The radiation imaging apparatusaccording to claim 3, further comprising a grid portion configured toeliminate scattered rays of the radiation, which is mounted on animage-receiving surface of the two-dimensional detection device, andwherein the radiation source shift unit moves the radiation source inthe direction orthogonal to a stripe direction of the grid portion. 5.The radiation imaging apparatus according to claim 2, furthercomprising: a detection device shift unit provided between thetwo-dimensional detection device and the second sub-arm and configuredto move the two-dimensional detection device towards the second sub-arm,wherein the detection device shift unit moves the two-dimensionaldetection device according to an angle of rotation of the second sub-armto maintain the two-dimensional detection device aligned with an imagingaxis that links the two-dimensional detection device, which has not yetbeen moved, and the radiation source.
 6. The radiation imaging apparatusaccording to claim 5, further comprising a grid portion configured toeliminate scattered rays of the radiation, which is mounted on animage-receiving surface of the two-dimensional detection device, andwherein the detection device shift unit moves the two-dimensionaldetection device in the direction orthogonal to a stripe direction ofthe grid portion.
 7. The radiation imaging apparatus according to claim2, further comprising: a radiation source shift unit, which is providedbetween the radiation source and the first sub-arm, configured to movethe radiation source towards the first sub-arm; and a detection deviceshift unit, which is provided between the two-dimensional detectiondevice and the second sub-arm, configured to move the two-dimensionaldetection device towards the second sub-arm, wherein the radiationsource shift unit moves the radiation source to maintain the radiationsource aligned with the imaging axis passing through the center of thetwo-dimensional detection device changed by the movement of the secondsub-arm, and wherein the detection device shift unit moves thetwo-dimensional detection device to maintain the two-dimensionaldetection device aligned with the imaging axis passing through thecenter of the radiation source changed by the movement of the firstsub-arm.
 8. The radiation imaging apparatus according to claim 2,wherein at least one of a connection portion between the first sub-armand the C-arm and a connection portion between the second sub-arm andthe C-arm can move along the frame of the C-arm.
 9. The radiationimaging apparatus according to claim 2, wherein the frame of the C-armis a semicircular frame having a central point located along an imagingaxis, wherein, when an angle α from a crossing portion of the imagingaxis, which links the two-dimensional detection device and the radiationsource, and the C-arm to the connection portion between the firstsub-arm and the C-arm or to the connection portion between the secondsub-arm and the C-arm at the central point of the semicircular frame ofthe C-arm is defined as α, the inequality of α1=<α=<α2 is established,and when a lower limit of an imaging distance due to the grid portion,which is provided on the image-receiving surface of the two-dimensionaldetection device to eliminate the scattered rays of the radiation, isdefined as f1, the radius of the semicircular frame of the C-arm isdefined as R, the distance from the connection portion between thesub-arm and the C-arm to the connection portion between the sub-arm andthe two-dimensional detection device or the radiation source is definedas L1, L1 is defined as a smallest value satisfying the followingequations (1) and (2) below, and the distance from the connectionportion between the sub-arm and the C-arm to the crossing portion isdefined as L2, the equations of:L1=L2   (1)2R=f1+L1×cos(α1)   (2)f1=R×(1+cos(α2))   (3) are satisfied.
 10. The radiation imagingapparatus according to claim 2, further comprising a conjunction unitconfigured to rotate the second sub-arm according to an angle ofrotation of the first sub-arm in conjunction with the first sub-arm or aconjunction unit configured to rotate the first sub-arm according to anangle of rotation of the second sub-arm in conjunction with the secondsub-arm.
 11. The radiation imaging apparatus according to claim 10,further comprising an input unit configured to input imaged-portioninformation, wherein the conjunction unit moves the first sub-arm or thesecond sub-arm in conjunction with the second sub-arm or the firstsub-arm based on the imaged-portion information input by the input unit.12. A control method in a radiation imaging apparatus that includes: aC-arm; a radiation source configured to irradiate a subject withradiation; and a two-dimensional detection device configured to detectthe radiation having passed through the subject, wherein the radiationsource and the two-dimensional detection device are arranged to faceeach other across the C-arm, wherein the radiation source is attached tothe C-arm via a first sub-arm that is rotatably connected to the frameof the C-arm at the inside from one end portion of the frame, and thetwo-dimensional detection device is attached to the C-arm via a secondsub-arm that is rotatably connected to the frame of the C-arm at theinside from the other end portion of the frame, a radiation source shiftunit provided between the radiation source and the first sub-arm andconfigured to move the radiation source towards the first sub-arm, and adetection device shift unit provided between the two-dimensionaldetection device and the second sub-arm and configured to move thetwo-dimensional detection device towards the second sub-arm, the methodcomprising: shifting the radiation source by the radiation source shiftunit, according to an angle of rotation of the first sub-arm, tomaintain the radiation source aligned with an imaging axis linking theradiation source, which has not yet been moved, and the two-dimensionaldetection device, or shifting the two-dimensional detection device bythe detection device shift unit, according to an angle of rotation ofthe second sub-arm, to maintain the two-dimensional detection devicealigned with an imaging axis linking the two-dimensional detectiondevice, which has not yet been moved, and the radiation source.
 13. Acontrol method in a radiation imaging apparatus that includes: a C-arm;a radiation source configured to irradiate a subject with radiation; anda two-dimensional detection device configured to detect the radiationhaving passed through the subject, wherein the radiation source and thetwo-dimensional detection device are arranged to face each other acrossthe C-arm, wherein the radiation source is attached to the C-arm via afirst sub-arm that is rotatably connected to the frame of the C-arm atthe inside from one end portion of the frame, and the two-dimensionaldetection device is attached to the C-arm via a second sub-arm that isrotatably connected to the frame of the C-arm at the inside from theother end portion of the frame, a radiation source shift unit providedbetween the radiation source and the first sub-arm and configured tomove the radiation source towards the first sub-arm, and a detectiondevice shift unit provided between the two-dimensional detection deviceand the second sub-arm and configured to move the two-dimensionaldetection device towards the second sub-arm, the method comprising:shifting the radiation source by the radiation source shift unit tomaintain the radiation source aligned with an imaging axis passingthrough the center of the two-dimensional detection device changed bythe movement of the second sub-arm, or shifting the two-dimensionaldetection device by the detection device shift unit to maintain thetwo-dimensional detection device aligned with an imaging axis passingthrough the center of the radiation source changed by the movement ofthe first sub-arm.
 14. A computer-readable storage medium storing aprogram that controls a radiation imaging apparatus that includes: aC-arm; a radiation source configured to irradiate a subject withradiation; and a two-dimensional detection device configured to detectthe radiation having passed through the subject, wherein the radiationsource and the two-dimensional detection device are arranged to faceeach other across a C-arm, wherein the radiation source is attached tothe C-arm via a first sub-arm that is rotatably connected to the frameof the C-arm at the inside from one end portion of the frame, and thetwo-dimensional detection device is attached to the C-arm via a secondsub-arm that is rotatably connected to the frame of the C-arm at theinside from the other end portion of the frame, a radiation source shiftunit provided between the radiation source and the first sub-arm andconfigured to move the radiation source towards the first sub-arm, and adetection device shift unit provided between the two-dimensionaldetection device and the second sub-arm and configured to move thetwo-dimensional detection device to the second sub-arm, the programcomprising: computer-executable instructions for shifting the radiationsource by the radiation source shift unit, according to an angle ofrotation of the first sub-arm, to maintain the radiation source alignedwith an imaging axis linking the radiation source, which has not yetbeen moved, and the two-dimensional detection device, orcomputer-executable instructions for shifting the two-dimensionaldetection device by the detection device shift unit, according to anangle of rotation of the second sub-arm, to maintain the two-dimensionaldetection device aligned with an imaging axis linking thetwo-dimensional detection device, which has not yet been moved, and theradiation source.
 15. A computer-readable storage medium storing aprogram that controls a radiation imaging apparatus that includes: aC-arm; a radiation source configured to irradiate a subject withradiation; and a two-dimensional detection device configured to detectthe radiation having passed through the subject, wherein the radiationsource and the two-dimensional detection device are arranged to faceeach other across a C-arm, wherein the radiation source is attached tothe C-arm via a first sub-arm that is rotatably connected to the frameof the C-arm at the inside from one end portion of the frame, and thetwo-dimensional detection device is attached to the C-arm via a secondsub-arm that is rotatably connected to the frame of the C-arm at theinside from the other end portion of the frame, a radiation source shiftunit provided between the radiation source and the first sub-arm andconfigured to move the radiation source towards the first sub-arm, and adetection device shift unit provided between the two-dimensionaldetection device and the second sub-arm and configured to move thetwo-dimensional detection device towards the second sub-arm, the programcomprising: computer-executable instructions for shifting the radiationsource by the radiation source shift unit to maintain the radiationsource aligned with an imaging axis passing through the center of thetwo-dimensional detection device changed by the movement of the secondsub-arm, or a shift step in which the detection device shift unit movesthe two-dimensional detection device to maintain the two-dimensionaldetection device aligned with an imaging axis passing through the centerof the radiation source changed by the movement of the first sub-arm.16. A radiation imaging apparatus comprising: a C-arm; a radiationsource configured to irradiate a subject with radiation; and atwo-dimensional detection device configured to detect the radiationhaving passed through the subject, wherein the radiation source and thetwo-dimensional detection device are respectively arranged on oppositeends of the C-arm so as to face each other such that an imaging axispassing through the ends of the C-arm links the focal point of theradiation source and the center of the two-dimensional detection device,and wherein at least one of the radiation source and the two-dimensionaldetection device is attached to the C-arm via a sub-arm that isrotatably connected to a frame of the C-arm at a predetermined distancefrom an end portion of the frame.